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1t4 Single tube receiver schematic clarification?

T23

Active Member
Apr 17, 2010
645
12
28
I dug up this old schematic off the net.....

It dates to 1948.

I am thinking about building it, I have the tube and should be able to get what else I need.

Also any guess as to what band this receiver covers?

http://vintageradio.me.uk/radconnav/valvetrf/SuperWidget1048sm%5Ccircuit.jpg

I just had two questions...

1. What is an Impax Coil as stated in the schematic?

2.What is the "75 MMF Ceramicon" component stated in the schematic?

T23
 

I dug up this old schematic off the net.....

It dates to 1948.

I am thinking about building it, I have the tube and should be able to get what else I need.

Also any guess as to what band this receiver covers?

http://vintageradio.me.uk/radconnav/valvetrf/SuperWidget1048sm\circuit.jpg

I just had two questions...

1. What is an Impax Coil as stated in the schematic?

2.What is the "75 MMF Ceramicon" component stated in the schematic?

T23

Not familiar with "Impax", but maybe someone from Europe can help. I'd guess it's an adjustable inductor that will resonate with the 200 pf tuner capacitor.

The other is a 75 micro-microfarad (known today as a 75 picofarad) ceramic capacitor.

I'd guess this will cover the AM broadcast band, based on the 200 "mmf" (or 200 pf) tuning capacitor. That will depend on the inductance of the coil.
 
In the early days many people would make that Impax coil by winding wire on an oatmeal or salt container. I think you'll find similar coils were used in many crystal radios back then and may be able to find more coil details from this. This Super Widget is very similar to the crystal receiver except it uses a tube as the detector. A noted improvement since it's powered and can easily drive the headphones. The coil is approximately 50 turns of wire. Usually every other wrap has the wire bent up in a U shape with the insulation removed. Using a jumper attached to the ground side of the coil, an alligator clip can be tapped at different points along the coil for various frequencies.
 
I was thinking about adjusting the component values to receive 20-40 meters?

I assume it would just be a matter of the coil, I have converted AM broadcast band receivers to 20-40 meters before by changing the inductance of the antenna coil.

I just haven't converted tube type receivers before.

T23
 
Using less turns on the coil and less capacitance on the tuner will increase the frequency. This type of radio lacks sensitivity and the problem will get worse at higher frequencies. It's only able to receive AM too so there will be nothing to hear on 20 meters if you could get it to work that high.
 
Looking at this circuit a little closer, I don't see any provision for detecting (removing the RF signal, leaving the audio). This is generally handled by a diode, but unless the tube is somehow supposed to detect and amplify the signal applied to the control grid, I don't quite see how this is going to work...
 
The Super Widget circuit is a variant of the Ultra Audion circuit which was stumbled upon by Lee deForest due to a wiring error.

UltraAudion2.gif


It is an early regenerative circuit, meaning it is very sensitive. I have seen this type of circuit being used as high as 40 meters and have heard of it being used at even higher frequencies. If this circuit were being used as a straight regenerative circuit, the grid leak and cap would be about 1M and 150pF or so. the odd values being used in the Super Widget circuit make it into a super regenerative circuit. It will automatically go into cut off when it starts to oscillate then back off, then start to oscillate again, etc. at a high frequency. That's how the 'super' part works. By using a 40pF tuning cap and a coil consisting of 20 turns of enameled 18 guage wire wound on a 1/2 inch form should get you to about 10 meters. Add more turns to get to 20 or 40 mters, or use a bigger tuning cap. I hope this helps!

Norman
KA1GUK
 
Last edited:
Thanks, strange thing is I just got some parts I needed for this project.

I got the socket I needed for the tube and I got some. Var. Caps in.


T23
 
This info may help, for those who want to build the radio to tune the MW AM broadcast band:

'The coil is wound on a pencil form and is 70 turns of Litz wire. More or less turns on the coil will allow the radio to tune different stations.'

'The chassis is made from thin aluminum and measures 3/4 x 1 7/16 x 2 1/4.'

This is per Alan McChesney, N2ZHS
 

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